We'll probably never colonize Mars or deep space - and here's why

The main reason is that Mars is a very unhealthy place, not just for humans but for all life. Forget the temperature extremes. The biggest problem with Mars for maintaining life is that it has almost no protection against radiation. It has no iron core like Earth and thus it does not have the magnetic field that protects humans from cosmic rays and solar mass ejections.

Six feet of soil can shield against cosmic rays as can a few centimeters of water. Since hauling water to Mars hardly seems practical, unless an ample water supply is found on Mars, the "explorers" will have to be satisfied with living and exploring under the surface.

Also, the human body is so adapted to our level of gravity that almost absent gravity (as in the space station) damages bone density. In a large space craft that rotates, you can use centrifugal force to simulate gravity, but how do you do that on the surface of Mars? Not exactly a vacation and no place anyone would want to live for long.

Terraforming isn't practical unless there's a way to give the planet a magnetic field. Otherwise, the atmosphere will simply be lost to space.

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We must tap renewable forms of energy and also nuclear. There are safer nuclear plants that are currently being develop. For instances a class of liquid metal reactor would never melt down. The fuel is already liquid.

Chapter 6 is all about the "Future of Space Travel." He talks about things like establishing a moon colony, visiting an asteroid, manned missions to mars, constructing a space elevator, what space travel might look like by 2100 as far as different types of propulsion and ship design, space tourism, and a few more subjects. The long and short of it is that we shouldn't expect to be colonizing space in the next 100 years.

One way to get into space permenently, would be to establish a beach head off world and start adapting technology to build what we need with available materials. Using Earth as a base of operations makes demands on energy supplies to excape the gravity well, and makes that off world population beholden to Earth and it's politics.

A separate 'corporate' or 'political entity' made up of folks willing to commit to an off world existence, might be a good way to begin, but would be fraught with power politics as it matures.

Such a group would not need Earth for energy, water, metals, food, etc once established, and could generate a profit from research, fabrication, travel, etc. Money could become unimportant in such an open, resource rich, albeit hostile, environment. Taping into the energy flux of the sun, possible water supplies on Mars/asteroids/Moon, liquid methane on some of the small satellites of Jupiter/Saturn, etc, could create opportunities only dreamed of.

I am much more optimistic. I think it is more about having a dream, getting off this rock, taking what we need, and being actually 'creative' with what we know and and can learn.

It might imply the need for some tax or penalty structure to control traffic.

I expect that duration of exposure to space environments with limited shielding might be hell on the first long term off-worlders. It might be that 'shielding' will be the most expensive or critical component for long term habitation. Maybe in the 'future' this will become a greater issue, as an occupational hazard. So far, we can mostly take our low radiation exposure for granted, but I expect that with the recent reactor explosion in Japan, this cavaler attitude will need to end.